The present invention relates to a video signal processor to which a sharpening circuit is preferably adapted in order to improve the sharpness of a picture, and a video signal processing method implemented in the video signal processor.
A sharpening circuit is a known means that has the ability to improve sharpness when adapted to a television receiver, a video tape player, or a digital video disk player.
A noise reducing circuit for the conventional television receiver includes a circuit that improves sharpness to make a noise indiscernible. Specifically, the circuit detects a noise level, adjusts a sharpness level in inverse proportion to the detected noise level, and increases a gain to be given to a relatively high-frequency signal component.
However, as far as the foregoing conventional noise reducing circuit is concerned, if a signal contains a noise, a sharpening circuit may intensify the noise. This may lead to deterioration of image quality. For this reason, another method adopts a circuit that detects a noise level, adjusts a sharpness level in inverse proportion to the detected noise level, and thus makes a noise indiscernible. In this case, the signal-to-noise ratio of a video signal cannot be improved directly. Moreover, there is a drawback that if a noise is present, sharpness cannot be improved but deteriorates.
The sharpening function includes a core ring sharpening technology that sharpens only a signal whose level is equal to or larger than a certain level but does not sharpen small-amplitude signals including a noise. However, the core ring sharpening technology has a drawback that a noise contained in a video signal cannot be eliminated.
Accordingly, an object of the present invention is to provide a video signal processor that successfully reduces the level of a noise contained in a video signal, and a video signal processing method implemented in the video signal processor.
A video signal processor in accordance with the present invention includes a sharpening circuit and a non-correlation detecting circuit. The sharpening circuit is capable of receiving an input luminance signal. The sharpening circuit has a transversal filter. The transversal filter is operable to filter the input luminance signal to produce an intermediate signal and to produce a filtered luminance signal having a time lag. The sharpening circuit is operable to multiply the filtered luminance signal by a predetermined factor to produce a weighted signal including the time lag, to adjust the time lag to produce a resultant luminance signal, and to add the resultant luminance signal to the intermediate signal. The non-correlation detecting circuit detects noise or fluctuation in the intermediate signal. The non-correlation detecting circuit is operable to set the predetermined factor to a selected value based upon the presence of at least one of the noise or the fluctuation in the intermediate signal. When the intermediate signal is detected by the non-correlation detecting circuit to contain the noise but not the fluctuation, the sharpening circuit performs noise canceling to subtract at least a portion of the noise from the resultant luminance signal.
A video signal processing method in accordance with the present invention includes sharpening and non-correlation detection. During sharpening, a transversal filter is used to filter an input luminance signal to produce an intermediate signal and to produce a filtered luminance signal having a time lag. The filtered luminance signal is multiplied by a predetermined factor to produce a weighted signal including the time lag. The time lag is adjusted to produce a resultant luminance signal. The resultant luminance signal is added to the intermediate signal. Non-correlation detection is performed on the intermediate signal to detect noise or fluctuation. The predetermined factor is set to a selected value based upon the presence of at least one of the noise or the fluctuation in the intermediate signal. When the intermediate signal is detected to contain the noise but not the fluctuation, noise canceling is performed to subtract at least a portion of the noise from the resultant luminance signal.
Moreover, a video signal processor in accordance with the present invention includes a sharpening circuit, a non-correlation detecting circuit, and a noise level detecting circuit. The sharpening circuit is capable of receiving an input luminance signal. The sharpening circuit has a transversal filter. The transversal filter is operable to filter the input luminance signal to produce an intermediate signal and to produce a filtered luminance signal having a time lag. The sharpening circuit is operable to multiply the filtered luminance signal by a predetermined factor to produce a weighted signal including the time lag, to adjust the time lag to produce a resultant luminance signal, and to add the resultant luminance signal to the intermediate signal. The non-correlation detecting circuit detects noise or fluctuation in the intermediate signal according to a threshold voltage. The non-correlation detecting circuit is operable to set the predetermined factor to a selected value based upon the presence of at least one of the noise or the fluctuation in the intermediate signal. The noise level detecting circuit detects a noise level. The threshold voltage is varied depending upon the noise level. When the intermediate signal is detected to contain the noise but not the fluctuation, the sharpening circuit performs noise canceling to subtract at least a portion of the noise from the resultant luminance signal.
Moreover, a video signal processing method in accordance with the present invention includes sharpening, non-correlation detection, and noise level detection. During sharpening, a transversal filter is used to filter an input luminance signal to produce an intermediate signal and to produce a filtered luminance signal having a time lag. The filtered luminance signal is multiplied by a predetermined factor to produce a weighted signal including the time lag. The time lag is adjusted to produce a resultant luminance signal. The resultant luminance signal is added to the intermediate signal. Non-correlation detection is performed on the intermediate signal to detect noise or fluctuation, according to a threshold voltage. The predetermined factor is set to a selected value based upon the presence of at least one of the noise or the fluctuation in the intermediate signal. During noise level detection, a noise level is detected. The threshold voltage is varied depending upon the noise level. When the intermediate signal is detected to contain the noise but not the fluctuation, noise canceling is performed to subtract at least a portion of the noise from the resultant luminance signal.
Accordingly, the present invention exerts the operation described below.
According to the present invention, in a video signal processor and a video signal processing method, non-correlation detection is performed in order to detect noise or fluctuation in an intermediate signal. When the intermediate signal contains the noise but not the fluctuation, noise canceling is performed in order to subtract out at least a portion of the noise.
According to the present invention, a signal containing noise has its sharpness improved through sharpening without deterioration of image quality while having the noise canceled.
Furthermore, according to the present invention, in a video signal processor and a video signal processing method, non-correlation detection is performed in order to detect noise or fluctuation in an intermediate signal. When the intermediate signal contains noise, noise canceling is performed in order to subtract out at least a portion of the noise. A signal is discriminated from noise based on a threshold voltage. The threshold voltage is varied depending on a detected noise level. Noise is subtracted from the luminance signal portion that contains noise based on the detected noise level.
According to the present invention, even when the level of noise varies largely, when noise is canceled, sharpness is improved without deteriorating image quality.